Towards the end of his long and industrious career, the literary jack-of-all trades Beverley Nichols (1898-1983) sat down to ponder the enticing topic of his reputation. No doubt about it, he briskly informed his friends, in 200 years' time he would be spoken of in the same breath as Jane Austen and Beatrix Potter. Naturally, there is still quite a long way to go before this prophecy is, or isn't, fulfilled, but one doesn't need a crystal ball to suspect that the odds on Nichols's Cats ABC or Down the Garden Path re-emerging as Penguin Modern Classics sometime in the 22nd century are rather on the long side.

On the other hand, in suggesting that the really vital critics of his work were not the newspaper reviewers or a galère of impressionable fans, but a pantheon of invisible readers crowded around some futuristic judgment seat whose criteria he could only guess at, Nichols was making an important point about literary reputations and how they endure. For the only reliable judge of a novel's merits, as Martin Amis once declared, is that grim and exacting arbiter, posterity, and, set against the reckonings of the future, present applause is only a little light murmuring heard a long way off.

The question of how the writer ends up with posterity on his, or her, side assumes an even sharper focus when you consider the fates of all the men and women of letters who have failed to pull off this Herculean feat. The English literary world of the last century is littered with the bones of once-gargantuan reputations now crumbled into dust. Whatever, for example, happened to Charles Morgan, a novelist taken immensely seriously in his 1930s heyday, and now all but vanished from the reference books, or Angus Wilson (1913-1991), knight of the realm and president of the Royal Society of Literature, the collected edition of whose works, urged into print by his admirers after his death, ended up in the remainder bins?

The vulnerability of practically any literary reputation south of, say, Shakespeare and Dante is nearly always confirmed by a glance at bygone novels in which aspiring writers talk about their role models. Patrick Hamilton's The Midnight Bell (1929), for instance, harbours a curious little scene in which Bob, the literary-minded barman, day-dreaming about the great masterpiece he intends to write, imagines that it will put him "in a class with Hugo, Tolstoy and Dreiser". No problem with the authors of Les Misérables and War and Peace, whose lustre shines triumphantly on, but Dreiser, whose An American Tragedy was hailed as a work of genius on its appearance in 1925, barely exists beyond a few US campus reading lists.

Even the notion of "canonic status", which still prevails in an increasingly cosmopolitan literary world no longer crowded out by dead white westerners, is no guarantee of survival. We take Dickens's longevity for granted, but there was a time in the 1880s when fashionable opinion tended to veer towards Thackeray as the greater mid-Victorian: the author of Great Expectations was thought "vulgar", unsubtle, and too fond of pandering to an upstart middle class. The same point could be made of Virginia Woolf in the 1950s, a decade so hostile to Bloomsbury and its legacy that Leonard Woolf declined to approve the idea of a Bloomsbury picture book on the grounds that reviewers would tear it to pieces.

The extraordinary revival in Woolf's fortunes that began in the early 1960s is a good example of how a modern literary reputation can be sustained, if the forces at work on its behalf are sufficiently powerful and tenacious. Although her readership had begun to pick up – annual sales of To the Lighthouse hit 20,000 copies in 1963 – the really serious interest came courtesy of American universities. Between 1960 and 1964, as Regina Marler relates in Bloomsbury Pie, her highly amusing study of the Bloomsbury industry, the number of academic monographs on Woolf and her work increased six-fold. It was in this atmosphere of scholarly graft that Michael Holroyd began on his two-volume life of Lytton Strachey, a work that transformed the Bloomsberries – at any rate in the public imagination – from a collection of high-minded pacifists into one of the most potent cultural alliances of the 20th century.

The fate of Leonard, Lytton and Virginia suggests that the real desideratum, when it comes to reserving your place in the pantheon, is an influential sponsor to plead your case. Sometimes this can be an energetic literary pressure group – Anthony Powell's reputation is kept green by the Anthony Powell Society, which organises conferences and lobbies for reissues; more often, a small but committed band of enthusiasts, quite often admiring fellow writers, labours to keep the work in print. If the rackety Soho boulevardier Julian Maclaren-Ross (1912-1964) or the novelist-cum-playwright Patrick Hamilton (1904-1962) still survive it is because there are enough well-placed fans eager to write prefaces to new editions and celebrate their publication with rapt encomia. Occasionally these lobbying campaigns can produce spectacular results. The modestly successful career pursued by Barbara Pym (1913-1980) crashed into the buffers the moment Cape turned down her seventh novel, An Unsuitable Attachment, in 1963. There followed a decade and a half of near obscurity, and plaintive letter-writing, until in 1977 the TLS advertised a survey bent on determining the most underrated writer of the 20th century. Both Philip Larkin and Lord David Cecil weighed in on her behalf, publishers found their interest mysteriously renewed, and Pym's next novel, Quartet in Autumn (1977) made the Booker shortlist.

And yet lobbying alone, however star-spangled the advocates, is rarely enough. If it were, the Norfolk farmer's wife Mary Mann (1848-1929) whose stories of the late 19th-century agricultural depression – for example, "Little Brother", which AS Byatt included in the Oxford Book of English Short Stories (1998) – have the edge on Hardy in their unrelenting determinism, would have a place in the late-Victorian canon next to George Moore and George Gissing. Here, naturally, the role of the publisher becomes crucial. One can think of half a dozen women writers – FM Mayor, Christina Stead, Brigid Brophy – who were kept alive by Virago press in the 70s, while the forward march of Gissing studies was kickstarted by the Harvester Press reissues masterminded by his legendary biographer, Pierre Coustillas.

It would be surprising, in what can sometimes seem the equivalent of a stockmarket, where shares in Iris Murdoch are in freefall while the bulls eagerly surround John Williams's Stoner, if a key role weren't played in all these manoeuvrings by simple chance. A director's decision to film or televise, if properly managed, can see a whole oeuvre rushed back into print. The push given to Brideshead Revisited by John Mortimer's 1981 TV adaptation boosted Evelyn Waugh's sales for the rest of the decade; by the mid-1980s his estate was generating a six-figure profit for his heirs. Or a hitherto neglected talent can suddenly find that circumstance has given their work a new relevance, as happened to John Christopher's eco-thrillers The Death of Grass (1956) and The World in Winter (1962), seized on by a new audience of environmentally conscious readers in the 2000s.

As chance, avid lobbying, or mysterious shifts in public taste propel certain writers back into the literary firmament, others are being sent inexorably on their way down. The usual explanation for a collapse in a writer's share price is that their books have begun to "date", to advertise a set of historical circumstances and emotional predicaments that no longer appeal to a contemporary audience. To most modern readers all those 1960s-era novels about unmarried mothers, however well-written, are no more than historical documents; the moral tocsin that clanged in the ear of the original purchasers has gone.

And yet the rules of literary "dating" are by no means clear-cut. If readers still enjoy the world of Barbara Pym, a landscape full of anxious curates and chattering spinsters, than why do they appear to have given up on Angus Wilson? I am an admirer of novels such as Hemlock and After (1952) and Late Call (1964), and my own – reluctant – answer would be that Wilson has dated in the wrong way, that his intensely particularised efforts to recreate the social environments of the late 1950s are more likely to appeal to social historians than novel readers, whereas Pym gets by on that tantalising abstract, charm. The same kind of superannuation is affecting Murdoch, whose abstruse and high-minded dialogue now seems as sepia-tinged in its way as the work of the forgotten Victorian titan George Meredith.

There is no point, of course, in turning reputation-broking into a kind of upmarket parlour game. To return to the stock market analogy, Northrop Frye was right to complain about a milieu in which "that wealthy investor, Mr Eliot, after dumping Milton on the market, is now buying him again". But the piece of advice habitually tendered to apprentice writers at the start of their careers – that books, in the end, find their level – can sometimes seem all too problematic. Did Mary Mann find hers? And if not, why not? Once again, we are back with chance, or rather economics. For Mann's best work, alas, was in the short-story form, which all publishers since Caxton have been chary of sponsoring. Come on Penguin Classics. You know my number. Pick up the phone.